Humans were there earlier - Evidence of the earliest human activity dates back to the first or second century BCE, according to Atlas Obscura. Little is known about the ancient race who inhabited the area.

Where did all that basalt come from? - The basalt stones are reported to have come from the opposite side of Pohnpei, from a volcanic plug where magma had hardened within the vent of an active volcano.

How was it transported? - Modern archeologists have no idea how the massive stones were moved from one side of Pohnpei to the other, then stacked so high, considering the primitive technology that would have been available at the time.

It rivals the work of the pyramids - The effort required to build the megalithic structures would have rivaled that of the Egyptian pyramids, Oddity reports, as the rocks had an estimated total weight of 750,000 metric tons.

Theories of transportation - Experts have suggested that rafts may have been used to transport the huge rocks to the reef, but there are still no theories for how they were originally moved from their far quarries or how they became those impressive structures.

A site for worship - The brothers wanted a place to build an altar so that they could worship Nahnisohn Sahpw, the god of agriculture, which is somewhat ironic since the islands are not fit for agriculture.

When sorcery makes sense - Most Pohnpeians reportedly still believe that the ancient city was the work of sorcery, as no other viable theory for how humans moved 750,000 metric tons of basalt has surfaced.

A sacred site - However it came to be, it is recognized as a sacred site founded by the Saudeleur dynasty, which was once populated by chiefs and priests, as well as commoners to serve them. Pictured is the Saudeleur dynasty tomb.

Contesting stories of how it ended - There are many tales of how the Saudeleur reign ended, but all of them attribute it to the legendary warrior Isokelekel in the 15th century, who, it’s said, implemented a new system of tribal chiefdom.

It's sometimes called "the ghost city” - The mystery of the ancient city’s origins and purpose has naturally inspired quite a few legends involving spirits and ghosts. Some are scared to visit, while others go precisely for the spook.

'Call of Cthulhu' - His short story mentions the real island of Pohnpei and uses the mythology of Nan Madol in his description of "The nightmare corpse-city of R’lyeh" which was "built in measureless eons behind history."

The mysterious prehistoric city built on a coral reef

The "Venice of the Pacific" has baffled scientists for years

In a remote region of the western Pacific Ocean lies a stunning and spooky unsolved mystery: the ruins of the ancient city of Nan Madol.

Located next to the eastern shore of Micronesian island Pohnpei, this once-great, prehistoric city is comprised of nearly 100 geometrically shaped man-made stone islands, and it’s the only ancient city built atop a coral reef.

No one is sure of the origins, nor why anyone would want to build a city far from food and water, and yet its ruins are rife with stories and spirits. Check out the gallery for a brief tour of the space and travel back in time.